I heard the Messenger of Allah ﷺ say, "When one of you spits phlegm in the mosque, let him bury it so that it does not land on a believer's skin or clothing and cause him harm."
سمعت رسول الله ﷺ يقول: إذا تنخم أحدكم في المسجد، فليغيب نخامته أن تصيب جلد مؤمن، أو ثوبه فتؤذيه.
Imam Ahmad (1543), Bazzar in Bahr Zakhkhar (1127), and Abu Yaala (808) all narrated it through various routes from Muhammad bin Ishaq, who said, Abdullah bin Muhammad bin Abdul-Rahman bin Abu Atiq told me, from Amir bin Saad, from his father, and he mentioned it.Bazzar said, "We do not know this hadith to be narrated from Saad except by this route, and we do not know anyone who narrated it from Amir bin Saad except Abdullah bin Muhammad bin Abdul-Rahman bin Abu Atiq."Haythami said in Majmaa (8/114), "Bazzar narrated it, and its narrators are the narrators of sahih."I say, it is as he said, except that he fell short in attributing it fully. Muhammad bin Ishaq is a mudallis, but he stated clearly that he heard it directly, and he is hasan al-hadith. Ibn Khuzayma graded it sahih (1311) and reported it through this same route.